Winter project: CaK doublestack

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bart1805
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Winter project: CaK doublestack

Post by bart1805 » Thu Oct 11, 2018 8:13 pm

Hi all,
A couple of months ago I bought a Lunt 60 CaK with a B600 diagonal. The scope is living with Pedro now. The filter is still here. I like the difficulties of CaK imaging and was tempted when Apollo posted about the Chroma Filters. But the new prices Bob mentioned meant that this road came to an end.
On a Dutch forum I posted a "wanted add" for a PST CaK. Within 24 hours I got offered 2 of them. Bought them both, first will arrive here in a couple of days, will pick the other one up in two weeks. So some modding to do this winter....

Here is the idea, completely stolen from others that have walked this path before.

a) 2 inch Baader Blue CCD
b) Astrodon 1,25 inch UVenus filter or 1,25 inch UV/IRcut on KG3 from Beloptik
c) option: Baader CaK filter, removed one of the filters because of the reflections, before the PST #1 filter
d) PST filter #1 on the nosepiece of a Skybender (I will be using it sooner than I thought Apollo)
e) PST filter #1 inside the Skybender

Camera used will be the ZWO ASI 290MM

Triple stacking would be with the Lunt B600 on the nosepiece of the camera. Looking forward to experiment with and without the Baader CaK Single / stacked / 2 single filters before both PST #1 filters, with or without the Lunt B600 etc.

Question.
When I look at the transmission curves the Astrodon UVenus filter seems to be a better candidate than the UV/IRcut on KG3. The UVenus drops immediately after 400nm. Any opinions about that? Another advantage is that I already have the UVenus filter.
CS! Bart.

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Re: Winter project: CaK doublestack

Post by marktownley » Thu Oct 11, 2018 8:59 pm

I think try what you've got already Bart.
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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Thu Oct 11, 2018 9:21 pm

stay clear of the U filter, it low transmission at 393 for what you want to do. get a secondary bandpass filter.

This one paired with the b-ccd filter will be killer, https://www.semrock.com/FilterDetails.a ... 01-Clin-25

also get ar coated kg3 from thorlabs

https://www.thorlabs.com/thorproduct.cf ... r=FGS900-A

you will be very happy with this trio combo..

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Re: Winter project: CaK doublestack

Post by Valery » Fri Oct 12, 2018 2:35 am

Double or triple or quadro stack will not gain enough in sun appearance in Ca K at a small scale. Good Lunt CaK filter is enough for small telescopes. The only gain will be prominences. The only real gain from DS or TS can be obtained only at super granulation cells level. However this require a telescope at least 6" in size. Better from 8". See the image taken by F. Rouviere (France) with his 210mm telescope and 5A Quark CaH. Even QUAD stacked 100mm scope will not come close in details to an 8" single stacked 5A(!) scope.


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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Fri Oct 12, 2018 3:19 am

Valery wrote:
Fri Oct 12, 2018 2:35 am
Double or triple or quadro stack will not gain enough in sun appearance in Ca K at a small scale. Good Lunt CaK filter is enough for small telescopes. The only gain will be prominences. The only real gain from DS or TS can be obtained only at super granulation cells level. However this require a telescope at least 6" in size. Better from 8". See the image taken by F. Rouviere (France) with his 210mm telescope and 5A Quark CaH. Even QUAD stacked 100mm scope will not come close in details to an 8" single stacked 5A(!) scope.


Valery
valery: do you place any filters before your safix? I will be using mine real soon for 393, is it best to cut my refractor tube by 150mm and use extension tubes for more control?

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Re: Winter project: CaK doublestack

Post by Valery » Fri Oct 12, 2018 6:01 am

Yes, I do use SAFIX after ERF

I don't know what is your 150mm refractor to tell you wha to do.


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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Fri Oct 12, 2018 6:22 am

Valery wrote:
Fri Oct 12, 2018 6:01 am
Yes, I do use SAFIX after ERF

I don't know what is your 150mm refractor to tell you wha to do.


Valery
150mm x 2250mm F/15

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Re: Winter project: CaK doublestack

Post by bart1805 » Fri Oct 12, 2018 7:22 am

Thanks guys.
@Valery: Bob made some comparisons between single and doublestack CaK with smaller scopes. I like the doublestack images more than the single stack. I know I would have to go bigger in the end. But first let me master this with a relatively small telescope (150mm f/8 Skywatcher). For planetary (mostly visual) I use a 9 inch Maksutov-Cassegrain. It is home build (not by me) and completely isolated (from the inside) to fight the tube currents. Optics Intes MK91, D=228 mm f/3100 mm. Maybe that will be my solar scope of the future.
@Mark: Yes you are right.
@Apollo: I will try the UVenus filter first and see what happens. But I think you are right that this filter dives just before 393nm.

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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Fri Oct 12, 2018 7:30 am

bart1805 wrote:
Fri Oct 12, 2018 7:22 am
Thanks guys.
@Valery: Bob made some comparisons between single and doublestack CaK with smaller scopes. I like the doublestack images more than the single stack. I know I would have to go bigger in the end. But first let me master this with a relatively small telescope (150mm f/8 Skywatcher). For planetary (mostly visual) I use a 9 inch Maksutov-Cassegrain. It is home build (not by me) and completely isolated (from the inside) to fight the tube currents. Optics Intes MK91, D=228 mm f/3100 mm. Maybe that will be my solar scope of the future.
@Mark: Yes you are right.
@Apollo: I will try the UVenus filter first and see what happens. But I think you are right that this filter dives just before 393nm.
i mean, it works. its the same as the baader planetarium U-filter. its ug11 substrate. You want to keep transmission as high as possible with those pst filters. especially two in the same telescope :)

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Re: Winter project: CaK doublestack

Post by Valery » Fri Oct 12, 2018 10:06 am

TheSkyBurner wrote:
Fri Oct 12, 2018 6:22 am
Valery wrote:
Fri Oct 12, 2018 6:01 am
Yes, I do use SAFIX after ERF

I don't know what is your 150mm refractor to tell you wha to do.


Valery
150mm x 2250mm F/15
If your objective is null corrected at 532nm (530 - 546nm range), then at 3933,7A it
should has 0,94 Strehl and so, no corrector needed.

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Re: Winter project: CaK doublestack

Post by Valery » Fri Oct 12, 2018 10:27 am

bart1805 wrote:
Fri Oct 12, 2018 7:22 am
I know I would have to go bigger in the end. But first let me master this with a relatively small telescope (150mm f/8 Skywatcher).
Bart,

You are a prisoner of illusions. If your 150mm F/8 achromat is nully corrected at a green light, say, at 530-546nm then Strehl ratio at the CaK line 393,4nm is only 0.09. It will just not work as needed for really high resolution. It's resolution at it's full aperture will corresponds to the resolution in a good 50-60mm scope. 100mm stop will give you 0,9 Strehl, 110m - 0.8 Strehl and 120mm stop - 0.63 Strehl. Most of barlows lenses should make things worser, some of them significantly worser.


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Re: Winter project: CaK doublestack

Post by bart1805 » Fri Oct 12, 2018 12:28 pm

Hi Valery, I am, as everybody, a prisoner of a whole lot of things, but not of illusions I hope. (-;
I know what the limits are of this set-up.

Right now I am the prisoner of a dilemma: do I have to use force on the gold tube first or on the blue collar? Order does not it matter?
Any advice?

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Re: Winter project: CaK doublestack

Post by pedro » Fri Oct 12, 2018 4:11 pm

I also have a PST CaK and I was unable to disassemble the telescope. Let us know how you get the PST CaK parts

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Re: Winter project: CaK doublestack

Post by bart1805 » Fri Oct 12, 2018 4:55 pm

Hi Pedro,
First try of removing the tube or the blue collar failed. Then I removed the six screws so I could take a look inside. Destroyed one of the screws so had to drill that one out. Then you see the pentaprism and the #2 filter. I think I can get the retaining ring loose without removing the pentaprism. Will try it later tonight, first have to do some soccer coaching.... If this works it is quite easy, so there must be something else that goes wrong tonight. (-;.
CS, Bart.

Edit: the kids had to wait five minutes and I have found the catch: I have the number 2 filter in my hands now. Not the #1....

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Re: Winter project: CaK doublestack

Post by christian viladrich » Fri Oct 12, 2018 6:16 pm

Hello Bart
Winter time is the right time for new project :-)
Please share us with some images of the inside of the PST.
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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Fri Oct 12, 2018 8:30 pm

christian viladrich wrote:
Fri Oct 12, 2018 6:16 pm
Hello Bart
Winter time is the right time for new project :-)
Please share us with some images of the inside of the PST.
dont use "the force", you are probably not a Jedi anyhow. its really simple to pop off. you need to use two clamps and a strap wrench. whatever pops off first is what happens the way it wants

then you do the same thing for the other part.

I clamped my pst black box down on the corner of a table, so the gold tube was off the right edge edge, then you just press down on the strap wrench and leverage does the rest.

When the gold tube is off, you do the same thing but on the opposite end, clamp down the gold tube so the piece you want is hanging off the edge. One is reverse threaded so it goes the opposite way. Takinging off the dew shield helps alot to make the gold tube flush with the table

Use a piece of rubber, like a balloon underneath so it doesn't slip

longer handle on the strap wrench = way more power and makes it super easy.

https://en.wikipedia.org/wiki/Strap_wrench

type of clamp
Image


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Re: Winter project: CaK doublestack

Post by MalVeauX » Fri Oct 12, 2018 8:52 pm

Hi Bart,

The 150mm F8 will work fine I think.

I have used a similar setup:

Celestron 150mm F8 achromatic refractor (CR150HD)
I masked it to 120mm to hit F10 for best use with PST CaK filters.
Skybender with 375~395nm filter (or a Chroma 393nm) (ERF #2) and Baader Blue CCD IR Block filter (ERF #1)
PST CaK filters (two of them) behind the skybender.
Then barlow/camera.

(image says 100mm mask, but it's 120mm):

Image

Results with 2x barlow, masked to 120mm at F10:

Image

Image

Image

Results with 3x barlow and no aperture mask, so 150mm at F8

Image

Very best,

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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Fri Oct 12, 2018 11:19 pm

MalVeauX wrote:
Fri Oct 12, 2018 8:52 pm
Hi Bart,

The 150mm F8 will work fine I think.

I have used a similar setup:

Celestron 150mm F8 achromatic refractor (CR150HD)
I masked it to 120mm to hit F10 for best use with PST CaK filters.
Skybender with 375~395nm filter (or a Chroma 393nm) (ERF #2) and Baader Blue CCD IR Block filter (ERF #1)
PST CaK filters (two of them) behind the skybender.
Then barlow/camera.

(image says 100mm mask, but it's 120mm):

Results with 2x barlow, masked to 120mm at F10:

Results with 3x barlow and no aperture mask, so 150mm at F8

Very best,

While stopping your scope down certainly does help it get to a slower F/ratio , and allows it to operate for better atmosphereic conditions. It unfortunately does not change the figure shape / radius curvature/ prescription of the lens itself.

A lens figured for F/8 stopped down to f/15 will not change the radius curvature. It will still be In the prescribed shape of f/8 glass.
I still agree that your images are awesome,

This is exactly why I bought the f/15 refractor 8 years ago. The lens prescription is high strehl for all wavelengths, if i mask it down it will maintain that same curvature.

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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Sat Oct 13, 2018 8:59 am

example of a 228mm x 1824mm F/8 refractor objective stopped down to 150mm (f/12) with a 1.3x barlow attached (f/15).

His f/15 images Looks about equal to your 150mm f/24 images Marty :)

He also has a 2.7x barlow set, (f40) It really shows how the barlow quality diminished between the two images as valery suggested.

viewtopic.php?f=4&t=24940

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Re: Winter project: CaK doublestack

Post by bart1805 » Sat Oct 13, 2018 11:58 am

christian viladrich wrote:
Fri Oct 12, 2018 6:16 pm
Please share us with some images of the inside of the PST.
pedro wrote:
Fri Oct 12, 2018 7:25 pm
Like Christian I would like to see some images of the mod
Hi Christian and Pedro, here they are:
viewtopic.php?f=9&t=25213

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Re: Winter project: CaK doublestack

Post by marktownley » Sat Oct 13, 2018 3:38 pm

bart1805 wrote:
Fri Oct 12, 2018 12:28 pm
Right now I am the prisoner of a dilemma: do I have to use force on the gold tube first or on the blue collar? Order does not it matter?
Any advice?
Another easier way; unscrew the retaining ring on the objective, pop out the objective cell, then use a 30cm steel ruler and you will be able to unscrew the retaining ring on the filter cell and then the filter you need for the mod will just pop out.
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Re: Winter project: CaK doublestack

Post by TheSkyBurner » Sat Oct 13, 2018 4:12 pm

marktownley wrote:
Sat Oct 13, 2018 3:38 pm
bart1805 wrote:
Fri Oct 12, 2018 12:28 pm
Right now I am the prisoner of a dilemma: do I have to use force on the gold tube first or on the blue collar? Order does not it matter?
Any advice?
Another easier way; unscrew the retaining ring on the objective, pop out the objective cell, then use a 30cm steel ruler and you will be able to unscrew the retaining ring on the filter cell and then the filter you need for the mod will just pop out.
the dew shield comes off the gold tube cleanly, without sacrificing the objective lens. Perhaps just try the dewshield first before the retainer ring! Then use the ruler as mark suggests
viewtopic.php?f=9&t=24604

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